The original Spaehkreuzer was to be armed with three turrets LDrh LC/38 (the 15cm lightweight twin) each weighting 60 tons. I expect the 20,3 cm single turret to weight ca. 46 tons. Overall the weight does not change much. The displacement of batch 1 spaehkreuzer was 6000 tons, beam was 15m, so I don't care about the punch of the guns. Finally there is the question of the usefulness. There is one good reason: range! The 15cm/48 TBK has a max range of 23500m, the 20,3cm/60 SK has a max range of 35000m. For comparision: the US-5"/38 has a max range of 16000m.
Well, if the design works, then why not? More helps more... it's germanish
So now the Z-66 with 8"singles with mag loader.
displacement: ca. 6000 tons empty, length: 152m oa, beam 14,9m , Performance: 110000 shp, max Speed: 36,2 kn, range: 12000 at 17 kn
armament: 4x203mm, 3x2x10,5cm aa, 4x4x2cm aa, 2x5 torpedotubes 53,3cm, waterbombs